Casual (and Fun) Communications

The other day, I received the most fun and eye-catching shipping confirmation from BetterWorldBooks:

Hello Tabita, 

(Your book(s) asked to write you a personal note - it seemed unusual, but who are we to say no?)
 
Holy canasta! It’s me… it’s me! I can’t believe it is actually me! You could have picked any of over 2 million books but you picked me! I’ve got to get packed! How is the weather where you live? Will I need a dust jacket? I can’t believe I’m leaving Mishawaka, Indiana already - the friendly people, the Hummer plant, the Linebacker Lounge - so many memories. I don’t have much time to say goodbye to everyone, but it’s time to see the world!

I can’t wait to meet you! You sound like such a well read person. Although, I have to say, it sure has taken you a while! I don’t mean to sound ungrateful, but how would you like to spend five months sandwiched between Jane Eyre (drama queen)and Fundamentals of Thermodynamics (pyromaniac)? At least Jane was an upgrade from that stupid book on brewing beer. How many times did the ol’ brewmaster have one too many and topple off our shelf at 2am?
 
I know the trip to meet you will be long and fraught with peril, but after the close calls I’ve had, I’m ready for anything (besides, some of my best friends are suspense novels). Just five months ago, I thought I was a goner. My owner was moving and couldn’t take me with her. I was sure I was landfill bait until I ended up in a Better World Books book drive bin. Thanks to your socially conscious book shopping, I’ve found a new home. Even better, your book buying dollars are helping kids read from Brazil to Botswana.

I don’t think I’ve ever read an entire shipping confirmation email before, but with this one, I just couldn’t stop reading. It was great! This got me thinking about customer communications and the question of “How casual is too casual?”. In this case, it was a B2C email, but BetterWorldBooks certainly conducts B2B business as well. I personally prefer companies who appear to be casual and un-stuffy, even if it is a B2B scenario. However, I’m not sure about everybody else.

So, what do you think? How casual is too casual? What is the best way to gauge your customer base to determine the right level of casual and fun vs. “professional” and boring?